Meet the rare cave-dweller with 414 legs

The millipede. Photo / Paul Marek,Virginia Tech

Millipedes, the little blunt-headed invertebrates with a habit of coiling up like baby ferns, rarely live up their name.

In Latin, millipede means "thousand feet," though the majority of the arthropods do not surpass the hundred-leg mark.

That is not to say these creatures want for feet. They have plenty. And a newly described species, which was found living alone in a small California cave, almost does the millipede name justice.

Sporting 414 tiny walking appendages, the creature - a single male specimen - boasted the second-highest number of legs of any animal species on the planet.

At a glance, the millipede in question might not look like much: a bit like a plastic-coated shoelace tip gone to fuzz. But appearances, even those of tiny pale worms, can be deceptive. Its 2cm-long body, as millipede experts recently reported in the journal Zookeys, was packed with quite an array of strange anatomy.

When they counted its segments under a microscope, the scientists discovered it had a whopping 207 pairs of legs. Where the ninth and tenth pair would sit, the creature had four gonopods - feet adapted for transferring sperm. (The millipede had, roughly speaking, four penises. How that might have played out with a female of this species was unclear, because the biologists did not find one.)

After the scientists sliced the bachelor male open, as they reported in the study, they found 200 pores dotting the length of his body. Some of those nozzles had an "unidentified secretion extruded from the opening," which the scientists speculated could be a defensive poison. The arthropod, which they named Illacme tobini, also lacked eyes. Its bristly mouth parts were "peculiar," and their shape suggested the animal may have lived on a diet of only fungus.

Discovering the single I. tobini was no easy feat. During a series of expeditions to caverns within California's Sequoia National Park, biologists surveyed the area for rare invertebrates from 2002 to 2004, and again from 2006 to 2009.

On only one occasion, on October 9, 2006, did a biologist find the completely new species. Cave biologist Jean Krejca was exploring a marble cavern when she snagged the animal and preserved it in alcohol.

Krejca sent the specimen to a scientist named Paul Marek. Marek, an entomologist at Virginia Tech, had found a close relative of I. tobini in a valley in San Benito County, California, also in 2006. Government scientists first reported that animal, I. plenipes, in 1926. A female millipede of its kind had 750 legs, a record that stands to this day. But until Marek found it again, the most-leggy creature had not been seen for 90 years.

Marek and his colleagues confirmed that both of the leggy wundercritters were related. "I never would have expected that a second species of the leggiest animal on the planet would be discovered in a cave [240km] away," Marek said in a news release.

There was no sign of another Illacme tobini between 2010 and 2012. Embarking on additional surveys, the biologists combed 63 other locations in the Sierra Nevada foothills and El Dorado National Forest. They flipped over decaying logs, ruffled through leaf litter and overturned large stones. They found plenty of other arthropods, like pseudoscorpions, flies and spiders. But, at least for the time being, it appears as though the many-legged millipedes have repeated their disappearing act.